The present invention relates to an improved breast prosthesis or mammary implant, of a type known per se, comprising a molded silicone shell or envelope in which an aperture formed in the shell for removal from the mold is subsequently sealed with a silicone patch, thus forming an internal lumen or lumens which can then be filled with a fluid or gel, by either the manufacturer or surgeon. In particular, the present invention relates to a breast prosthesis thus formed with a substantially seamless join between the patch and the lumen.